Shawn Evans scored the game winner 10:05 into extra time as the Calgary Roughnecks earned first place in the West Division with a thrilling 12-11 victory over the Rush.
"It was such a relief to score that goal. We had fought so hard for this win," said Evans, who added nine assists in the game to set a new franchise record for points in a season with 112.
"It was an unbelievable game. Both teams were unbelievable. The defence ... 10 minutes without a goal in overtime. We had one goal in the third quarter. It's tough to describe what it's like to battle back to win this one."
Daryl Veltman scored five goals for the Roughnecks (9-7), who have guaranteed themselves home-field advantage for the first two rounds of the post-season should they advance that far.
Curtis Dickson had a two-goal game and Travis Cornwall, Scott Ranger, Jeff Shattler and Geoff Snider also scored for Calgary, which opens the playoffs Saturday at home to the Colorado Mammoth.
"It was such a good game of lacrosse," said Calgary coach Curt Malawsky. "It went back and forth all night long. We knew it was likely going to be a one-goal game. We just needed to hang around. They came out with a real quick start and we just had to weather the storm. That just showed the resilience of our guys not to panic. ...
"There was a lot on the line for both teams and both clubs laid it out there. The entire province of Alberta can be proud of that game. It was just phenomenal."
Alex Turner and Corey Small each had two-goal games for the Rush (9-7), who visit the Washington Stealth on Saturday.
Zack Greer, Curtis Knight, Brett Mydske, Mark Matthews, Ryan Ward, Jarrett Davis, and Jeremy Thompson also scored for Edmonton.
"I've never really come out of a game feeling like I do right now," said an exhausted and banged-up Matthews. "So they did a pretty good job, obviously, banging around and we played well, we just couldn't come out with a win. I thought we had it there, a couple pipes and it goes our way."
The Rush went from having a chance to finish first overall in the league to ending up third in the West and without a home playoff date as a result of Washington's 17-13 win over Philadelphia later in the night. Edmonton has never had a home playoff game in its seven years as a franchise.
"There's lots of lacrosse left," said Rush head coach Derek Keenan. "There's lots of opportunity ahead. If we win in Washington and Calgary loses at home, we're back here. And if that's the case and we win, then the final could be here."
Edmonton got on the board just 40 seconds in as Greer scored his 28th of the season on Roughnecks goalie Mike Poulin.
The Rush got another early goal from Turner but Calgary quickly replied on a marker by Veltman to make it 2-1.
The Rush opened it up for a 5-1 lead at the end of the first quarter as Knight picked the corner on the power play and Mydske and Matthews followed it up to give Edmonton the commanding lead.
Edmonton went up 6-1 three minutes into the third, but the Roughnecks came storming back to make it a one-goal game on scoring strikes by Veltman, Ranger, Dickson and Cornwall.
The teams traded goals twice late in the third to leave Edmonton clinging to an 8-7 lead at the midmark.
Both squads clamped down on defence in the third, as only three goals were scored. Two of them were by Small for the Rush to put Edmonton up 10-8 heading into the final frame.
Calgary closed to within one seven minutes into the fourth quarter as Veltman scored his fourth of the game on a diving shot.
The rivals traded goals just five seconds apart with six minutes to play, as Edmonton's goal from Turner and Calgary from transition player Snider made it 11-10.
The Roughnecks tied the game with just 1:39 to play on Veltman's fifth goal of the game.
Calgary then hit the post with just two seconds left to send the game to overtime.
Edmonton hit a post of its own two minutes into extra time.
Notes: There is no question which team has had the better of the overall series as Calgary came into the game with an impressive 22-4 all-time record over the Rush. However, Edmonton is 2-0 in playoff meetings between the teams. ... Edmonton rookie and 2012 first overall draft pick Mark Matthews set a new club record with his 38th goal of the season. Chris Gill set the mark of 37 in 2006 ... Calgary entered the match having scored a league-high 210 goals, but had allowed a second-worst 200 goals, compared to Edmonton's second-fewest 158 ... Roughneck forward and second leading-scorer Dane Dobbie was a late scratch for the contest with a knee injury ... Edmonton's Aaron Bold and Calgary's Mike Poulin came into the game tied for second amongst NLL goaltenders with eight wins apiece ... The Rush were 9-0 when leading after three quarters and 8-2 when leading at halftime coming into the final regular season game for both teams.